1. Field of the Invention
The present invention relates generally to a composite substrate, and more particularly to an innovative one which is configured into an electronic type. The present invention also relates to an LED heat-conducting substrate and its thermal module, and more particularly to an innovative one which is made of metal or carbon heat-conducting wire or fiber and insulating material having higher thermal conductivity and insulation property.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
An active LED may generate heat energy due to relatively low transfer efficiency of electric energy to optical energy. As for a high light intensity, high-power LED that generates more heat energy, if the heat energy cannot be released, the temperature of the LED will rise, leading to its color bias and degradation.
As a priority of design for LED, heat dissipation means heat energy is transferred from heat-conducting material to a heat exchanger, and then dissipated into the air via larger surface area of the heat exchanger. Said heat exchanger generally consists of extruded aluminum or die-casting fins, permitting the transfer of heat energy to the surface of fins using high heat transfer characteristic of aluminum and then enabling heat exchange with air. In practice, several LEDs form a light source, so a module structure is required to be configured with several LEDs, and these LEDs and power circuit are welded onto a circuit board with stronger heat-conducting capability, so that the heat energy of LED can be transferred to a heat exchanger while avoiding temperature rise and damage of components.
Heat transfer design required for LED generally encompasses chip package and module structure, both of which are provided with a substrate for connecting with the LED electrode and heat conduction. The substrate for chip package is taken as the carrier of LED chip to obtain higher heat transfer property, and made of high conducting and insulating materials such as: alumina, AIN, diamond-plated metal membrane, aluminum-containing silicon carbide or diamond composites, as disclosed in patents JP2000297301, JP2000303126, TW224873 and JP2003073169. In order to realize higher compactness of the interface contact and reduce thermal resistance of heat conduction generated from the interface, a heat-conducting layer is fabricated directly onto the semi-conductor substrate, or thermal stress is cut down through the composite design of heat-conducting layer, as disclosed in patents US2005070048, JP2005072069, JP2006060247, JP2006190705 and US708359. In addition, some through-holes are drilled onto the substrate to dissipate the heat quickly, and high heat-conducting materials (e.g.: metal bond) are filled into the through-holes, as disclosed in patents JP2002289747, JP5090437 and US2006006524. Moreover, the electrode pad of LED chips is welded by metal sheets to dissipate the heat energy, as disclosed in patents JP2009266972, JP2009194277 and JP2009188308. Due to the small size of substrate for chip package, ceramic material of higher insulation and thermal conduction can be used in collaboration with the through-holes to fabricate a heat-conducting channel, such that the packaged LED is provided with a high heat-conducting structure. Furthermore, the heat from chips can be dissipated from a conducting weld connected at bottom of the chips, as disclosed in patents US20100110692 and US20070176182.
The packaged LED is provided with a terminal electrode or metal electrode pins and conductive contact, so welding electrode and conductive contact are available for assembly of LED circuit board, making it possible for electrical connection and heat dissipation through the circuit board. Generally, the circuit board is provided with multiple LEDs, so it is sized bigger than the chip package substrate. PCB is commonly used in view of poorer mechanical strength of ceramic substrate. Made of phenolic resin and glass fiber, PCB has a heat conductivity lower than 0.5 W/m° K, but encounters a temperature rise problem for high-power applications. To improve heat conduction efficiency, a metal substrate coated with insulating layers at both sides is generally adopted, as disclosed in patents US20080057333, JP2004047863, US2009151982, US20080190542, JP2009123980 and JP2008159827. In addition, the substrates made of crystalline polymer with thermoset and thermoplastic organic materials are introduced to improve the heat conductivity, which contain metal powder or nitride fiber of high thermal conductivity, as disclosed in patents US2008057333, JP2008060535, JP2006165158, JP2154049, JP2004165421, KR20080028258, US2008073623 and JP2008081722. However, the heat conduction coefficient of the substrates made of polymer organic materials is difficult to reach 5 W/m ° K. Due to better heat conductivity than organic materials, the porous ceramic materials can be filled into the holes to improve the heat conduction effect, as disclosed in patents US20090290362 and JP2007173536, etc.
LED substrates generally consist of electrode and heat-conducting contacts. Despite the high heat conductivity of metal materials, a short circuit may occur if the electrode is directly welded onto metal substrates, so a metal surface must be provided with an electrical insulator. Except for diamond and nitride, the insulating materials present poor heat conductivity and resistance to mechanical impact. In such a case, the problems of high cost and poorer resistance to mechanical impact are confronted if high heat-conducting insulative substrate is applied. If low-cost PCB is used as the substrate, it is not suitable for high intensity lighting due to poor heat conductivity. If insulating film of poor heat conductivity is coated onto the metal substrate, the composite substrate's heat conductivity is relatively poor. With the growing market demand, the cost of high-power LEDs must be reduced; hence, the technical development is focused on the substrate serving as LED electrode pad having lost cost and high heat conductivity.
Thus, to overcome the aforementioned problems of the prior art, it would be an advancement if the art to provide an improved structure that can significantly improve the efficacy.
Therefore, the inventor has provided the present invention of practicability after deliberate experimentation and evaluation based on years of experience in the production, development and design of related products.